Assessment of cement paste properties using seawater: Early-age behavior, mechanical and microstructural analysis

Freshwater scarcity is an increasing challenge for the construction industry, which uses large volumes of potable water for concrete production. This study evaluates seawater as a sustainable alternative to tap water in cement paste, focusing on fresh properties, mechanical performance, and microstructural characteristics. Results showed that seawater accelerated hydration, with the peak heat flow reaching 3.42 mW/g at 9 h compared to 2.45 mW/g at 11 h for tap water, and reduced initial setting time by ∼60 min. Early-age strengths improved substantially, with compressive and flexural strengths increasing by 49.6 % and 46.4 % at 1 day, respectively, although 28-day strengths declined (-2.3 % compressive, −22.4 % flexural). XRD confirmed Friedel’s salt formation in seawater specimens, while SEM-EDS revealed higher chloride-bound phase and a greater presence of micropores in seawater paste. CT scanning quantified a higher void volume fraction in seawater paste (1.16 %) than in tap water paste (0.67 %). The integration of quantitative setting time and heat of hydration data with strength measurements, and their linkage to porosity characteristics derived from SEM–EDS and the relatively less explored CT analysis in this context, establishes a coherent microstructure-to-property framework. This combined approach paves the way for sustainable and time-efficient construction, with challenges in workability and durability mitigated by careful scheduling and admixture use.